A design method for the thickness of the socket of a socket-and-spigot pipe

Abstract

The present invention discloses a design method for the thickness of the spigot of a spigot-and-socket pipe, comprising the following steps: step S1: obtaining the differential equation of radial deformation of the ring and the general solution of the differential equation according to the deflection curve differential equation and the moment balance equation of the ring; step S2: calculating and obtaining the calculation formula of the maximum radial deformation of the ring according to the general solution of the differential equation obtained in step S1; step S3: obtaining the minimum spigot thickness of the base pipe that meets the deformation requirements according to the calculation formula of the maximum radial deformation obtained in step S2. The present invention can obtain the minimum spigot thickness of spigot-and-socket pipes of different pipe diameters that meet the deformation requirements through theoretical analysis and calculation, providing a reference for secondary processing and installation of pipes. The design method is a theoretical calculation with low cost and high efficiency, providing strong support for experiments and pipe design.

Description

Technical Field

[0001] The invention belongs to the technical field of pipe design, and in particular relates to a method for designing the thickness of a spigot-type pipe. Background Art

[0002] Most of the water pipes in the water supply and drainage systems for life and production are socket-type pipes, with a socket at one end and a spigot at the other end. During installation, the spigot of one pipe is inserted into the socket of another pipe and sealed with a seal to achieve the connection of each pipe in the pipe network. For water supply pipes in normal use, they will be subjected to a large internal water supply pressure, which is a positive pressure, so the pipes must meet the specified strength requirements. Some existing standards (group standards and national standards) specify the nominal wall thickness under different pressure levels and different nominal diameters. Pipes that meet the standards can meet the strength requirements within the corresponding pressure level range. Therefore, the pipes produced by existing pipe manufacturers generally meet the requirements of the corresponding standards.

[0003] However, when a pipe network fails, for example, a pipe bursts in the pipe network, water in the pipe network will spray out from the burst, and the pressure in the pipe network will drop rapidly, even forming negative pressure. In addition, the pipe will also be subject to some external pressure, for example, the pipe buried in the soil will be subject to the gravity of the soil above it. Under the above external pressure and internal negative pressure, the pipe will deform radially. If the deformation of the socket is too large, the socket will separate from the socket connected to it, causing leakage at the connection between the socket and the socket, causing the inside of the water pipe to be contaminated. Therefore, it is necessary to ensure that the deformation of the socket of the pipe does not exceed a certain range under the above circumstances. To this end, for the socket, the minimum socket thickness that meets the deformation requirements must be obtained. If the socket thickness of the selected pipe is less than the minimum socket thickness that meets the deformation requirements, measures need to be taken to make it meet the deformation requirements. For example, during the secondary processing or installation of the pipe, an annular reinforcement ring is sleeved on the socket to enhance the ability to resist deformation. Summary of the invention

[0004] In view of the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a design method for the socket thickness of a socket-type pipe. The minimum socket thickness of socket-type pipes of different diameters that meets the deformation requirements can be obtained through theoretical analysis and calculation, thereby providing a reference for the secondary processing and installation of the pipe. The design method is a theoretical calculation with low cost and high efficiency, which provides strong support for experiments and pipe design.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for designing the thickness of a spigot-type pipe comprises the following steps:

[0007] Step S1: obtaining the differential equation of radial deformation of the ring and the general solution of the differential equation according to the deflection curve differential equation and the moment balance equation of the ring;

[0008] Step S2: Calculate and obtain a calculation formula for the maximum radial deformation of the ring according to the general solution of the differential equation obtained in step S1;

[0009] Step S3: The minimum thickness of the socket of the base pipe that meets the deformation requirements is obtained according to the calculation formula of the maximum radial deformation obtained in step S2.

[0010] As a further improvement of the above technical solution:

[0011] The calculation formula for the maximum radial deformation of the annulus obtained in step S2 contains an unknown coefficient, which is introduced in consideration of the internal negative pressure that the pipe bears during testing and failure.

[0012] Step S2 includes the following steps:

[0013] Step S21: Assuming that the annular ring is subjected to at least two radial concentrated forces that are symmetrical relative to the center of the circle, based on the assumption, calculating the constant term in the general solution of the differential equation to obtain the first form of the differential equation;

[0014] Step S22: Based on the first form of the differential equation obtained in step S21, assuming that the annulus is subjected to only two radial concentrated forces that are symmetrical relative to the center of the circle, the first form of the differential equation is transformed into a second form of the differential equation;

[0015] Step S23: introducing the internal negative pressure of the annulus into the second form of the differential equation by introducing a coefficient, so as to obtain the third form of the differential equation;

[0016] Step S24: Obtain a calculation formula for the maximum change in the diameter of the ring with a coefficient according to the third form of the differential equation obtained in step S23.

[0017] In step S3, the minimum thickness of the socket that meets the deformation requirements is calculated based on the provisions of the allowable deformation of the pipe and the formula obtained in step S2.

[0018] Step S3 includes the following steps:

[0019] Step S31: Calculating parameters of a reference pipe according to an existing shear load formula, wherein the material and outer diameter of the reference pipe are respectively the same as the material and outer diameter of the base pipe;

[0020] Step S32: obtaining the maximum deformation of the reference pipe socket through simulation according to the parameters calculated in step S31;

[0021] Step S33: Substituting the maximum deformation of the socket obtained in step S32 into the calculation formula of step S2 to obtain the coefficient value in the calculation formula, thereby obtaining a calculation formula for the maximum radial deformation of the ring with a known coefficient;

[0022] Step S34: Calculate the minimum thickness of the base pipe socket that meets the deformation requirements according to the national standard allowable deformation regulations and the formula obtained in step S33.

[0023] In step S1, the differential equation of the radial deformation u is obtained as: , its general solution is:

[0024] ,

[0025] Wherein, R is the average value of the outer radius and the inner radius of the ring; E is the elastic modulus of the tube, Pa; I is the moment of inertia of the tube section, m 4 ; M is the bending moment borne by a certain section of the ring in the local area, unit N*m; establish a two-dimensional coordinate system, It is the angle between the line connecting the point where the deformation amount is u and the origin of the coordinate system and the positive direction of the x-axis in the two-dimensional coordinate system. ; A1, A2, A3, B2, B3 are constants.

[0026] Assuming that the external force on the ring is symmetrical, the deflection curve equation is:

[0027] .

[0028] In step S2, it is assumed that the ring is subjected to at least two radial concentrated forces P that are symmetrical relative to the center of the circle, and the angle between two adjacent radial concentrated forces P is , the ring satisfies the following three boundary conditions:

[0029] (1) Because of symmetry, The rotation angle of the cross section at is 0, which satisfies the following formula:

[0030] ;

[0031] (2) Due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is,

[0032] ;

[0033] (3) Cutting near point A, removing point A and the acting force P, it can be seen from the symmetry and equilibrium conditions that the shear force on the cross section of the circular cut is , that is:

[0034] ;

[0035] Combining the above three formulas with the general solution of the differential equation, we get the first form of the differential equation:

[0036] ;

[0037] Assuming that the ring is subjected to only two radial concentrated forces P symmetrically relative to the center of the circle, then , we get the second form of the differential equation:

[0038] ;

[0039] Introducing the coefficient m, we get the third form of the differential equation:

[0040] ;

[0041] Point of application of force P The point is the point of maximum deformation, and the change in the diameter of the ring is:

[0042] .

[0043] The shear load formula used in step S31 is:

[0044] ,

[0045] Where: W is the shear load, in Newton (N); F is the shear force acting on the interface, in Newton (N); M P is the weight of the test component pipe and the weight of the object in the pipe, in kilograms (kg); a is the distance between the shear load application point and the end face of the socket inserted into the socket, in millimeters (mm); b is the distance between the center of gravity of the socket end pipe and the end face of the socket inserted into the socket, in millimeters (mm); c is the distance between the support point of the pad and the end face of the socket inserted into the socket, in millimeters (mm).

[0046] F=30×DN, E=200GPa, I=S 3 / 12, where DN is the nominal diameter of the pipe, S is the socket thickness, and the socket thickness used in calculating the coefficient m is the nominal wall thickness under the nominal diameter.

[0047] The beneficial effects of the present invention are as follows: the minimum thickness of the socket of the spigot-and-socket pipes of different diameters that meets the deformation requirements can be obtained through theoretical analysis and calculation, providing a reference for secondary processing and installation; if the thickness of the socket of the pipe is less than the minimum thickness, the socket thickness can be increased by installing a reinforcing ring at the socket so that the socket meets the deformation requirements; the pipes and pipe network systems installed in this way are more reliable to use, greatly reducing the leakage and water supply pollution caused by the separation of the socket and the socket of the adjacent pipe due to excessive deformation of the socket when the pipe bursts; the design method is a theoretical calculation with low cost and high efficiency, providing strong support for experiments and pipe design. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of the deformation of a circular ring before and after being subjected to a pair of radially symmetrical concentrated forces.

[0049] Figure 2 for Figure 1 Schematic diagram of local analysis.

[0050] Figure 3 Schematic diagram of a circular ring subjected to multiple uniformly arranged radial concentrated forces.

[0051] Figure 4 This is the stress analysis diagram of socket-type pipe. DETAILED DESCRIPTION

[0052] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0053] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0054] A method for designing the thickness of a spigot-type pipe comprises the following steps:

[0055] Step S1: According to the differential equation of the deflection curve of the ring and the moment balance equation, the differential equation of the radial deformation u of the ring and the general solution of the differential equation are obtained; because the cross-section of the pipe body and the socket of the pipe is a ring, the deformation of the socket is analyzed by analyzing the radial deformation of the ring. In addition, a cylinder of unit length can be regarded as a ring.

[0056] Step S2: Calculate and obtain a calculation formula for the maximum radial deformation of the ring according to the general solution of the differential equation obtained in step S1.

[0057] Step S3: The minimum thickness of the socket of the base pipe that meets the deformation requirements is obtained according to the calculation formula of the maximum radial deformation obtained in step S2. The base pipe refers to the pipe in the factory setting, and the base pipe is not installed with a reinforcement ring, and is not subjected to secondary processing such as a composite process. The base pipe includes a socket, a pipe body and a socket connected in sequence, and the outer diameter of the base pipe is the outer diameter of the pipe body.

[0058] The following is a detailed introduction to each step.

[0059] In step S1, the differential equation of the radial deformation u is obtained as:

[0060] (1)

[0061] Where R is half of the sum of the outer radius and the inner radius of the ring. In other words, R is one quarter of the sum of the outer diameter and the inner diameter of the ring. E is the elastic modulus of the pipe, Pa. I is the moment of inertia of the cross section of the pipe, m 4 M is the bending moment of a certain section of the ring in the local area, in N*m. Establish a two-dimensional coordinate system, It is the angle between the line connecting the point where the deformation amount is u and the origin of the coordinate system and the positive direction of the x-axis in the two-dimensional coordinate system. In this embodiment, an xy coordinate system is established, and point O is the origin of the coordinate system and the center of the ring. Figure 1 As shown. The radial deformation at point m1 is u, then the angle between om1 and the positive direction of the x-axis is .

[0062] The above differential equation (1) is obtained as follows:

[0063] like Figure 1 and 2 As shown in the figure, the dotted line is the circular ring that has not been deformed by external force, and the solid line is the shape of the circular ring after being deformed by two symmetrical radial external forces P. The position of the center point O of the circular ring remains unchanged before and after the deformation. Figure 1 In the figure, point O is also the vertex of the xy coordinate system, points m and n are two points on the ring before deformation; points m1 and n1 are two points on the shape of the ring after deformation, and points m1 and n1 are located on line segments om and on, respectively. It is the angle between the line connecting the point where the deformation is u and point O and the positive direction of the x-axis. The angle between om and on is , let u be positive when moving centripetally. Figure 2 In the equation, the line m1t passes through the point m1 and is perpendicular to the line segment om, and the line m1t1 is the tangent line passing through the point m1. The line n1t' passes through the point n1 and is perpendicular to on, and the line n1t1' is the tangent line passing through the point n1.

[0064] Arc before deformation mn The arc length is ds , whose curvature is k 1 , arc after deformation m 1 n 1 The curvature is k 2 , du Yes m and Point n The difference in radial deformation is The arc before deformation mn exist m Tangent line of point and n The angle between the tangent lines of a point, The deformation amount is u The radius corresponding to the point at after deformation is, Is an arc mn Deform to Arc m 1 n 1 back ds The increment of The arc after deformation m 1 n 1 exist m 1 Tangent line of point and n 1 The angle between the tangent lines of the point is m 1 t 1 and The angle between , then:

[0065] (2)

[0066] (3)

[0067] (4)

[0068] (5)

[0069] The angle between m1t1 and m1t is equal to , the angle between n1t1' and n1t' is equal to .

[0070] The variable of the rotation angle from section m1 to section n1 is :

[0071] (6)

[0072] Among them, the m section is the section passing through om and perpendicular to the ring. In other words, the m section is the section passing through the center axis of the tube corresponding to the ring and point m. Similarly, the n section is the section passing through on and perpendicular to the ring. In other words, the n section is the section passing through the center axis of the tube corresponding to the ring and point n. The angle between m1t1 and m1t is the rotation angle of the m1 section, and the angle between n1t1' and n1t' is the rotation angle of the n1 section.

[0073] Substituting formula (5) and (6) into formula (4) yields:

[0074] (7)

[0075] By series expansion we have:

[0076] Ignoring the higher-order terms, substituting the series expansion into (7) yields:

[0077] (8)

[0078] Substituting (2) into (8), we obtain:

[0079] (9)

[0080] Omitting the higher-order terms, we get: (10)

[0081] For a thin ring (i.e. a ring with a small difference between the outer diameter and the inner diameter relative to the diameter), we have: , by definition: ,therefore, , substituting into (10) we get, , combining formula (2) to obtain the differential equation formula (1) for radial deformation u.

[0082] The general solution of the above differential equation (1) is:

[0083] (11)

[0084] Among them, A1, A2, A3, B2, B3 are constants. If the external force is symmetrical, the odd function terms in the solution can be deleted, and the deflection curve equation is:

[0085] (12)

[0086] Step S2: Calculating and obtaining a calculation formula for the maximum radial deformation of the ring according to the general solution of the differential equation obtained in step S1, comprising the following steps:

[0087] Step S21: Assume that the annulus is subjected to at least two radial concentrated forces P that are symmetrical relative to the center of the circle. Based on this assumption, calculate the constant term in the general solution of the differential equation to obtain the first form of the differential equation.

[0088] Step S22: Based on the first form of the differential equation obtained in step S21, assuming that the annulus is subjected to only two radial concentrated forces P that are symmetrical relative to the center of the circle, the first form of the differential equation is transformed into the second form of the differential equation.

[0089] Step S23: Introduce the internal negative pressure on the annulus into the second form of the differential equation by introducing coefficients to obtain the third form of the differential equation.

[0090] Step S24: Obtain a calculation formula for the maximum change in the diameter of the ring with a coefficient according to the third form of the differential equation obtained in step S23.

[0091] In step S21, it is assumed that the ring is subjected to at least two radial concentrated forces P symmetrically relative to the center of the ring, and the radial concentrated force P means that the direction of the force P is radial to the ring and points to the center of the ring, and the angle between two adjacent radial concentrated forces P is ,like Figure 3 shown. Figure 1 The circular ring shown in FIG. 1 is subjected to two radial concentrated forces P which are symmetrical relative to the center of the circle, and the two radial concentrated forces P are located on the y-axis.

[0092] The ring satisfies the following three boundary conditions:

[0093] (1) Due to symmetry, the rotation angle of the section at this location is 0, which satisfies the following formula:

[0094] (13)

[0095] (2) Due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is,

[0096] (14)

[0097] (3) Cutting near point A, removing point A and the acting force P, it can be seen from the symmetry and equilibrium conditions that the shear force on the cross section of the circular cut is , that is:

[0098] (15)

[0099] in, dM represents the differential with respect to M. It should be noted that point (3) is not a real cut of the ring, but an assumption.

[0100] Simultaneously formula (13), (14), (15), the solution is:

[0101] (16)

[0102] (17)

[0103] (18)

[0104] Substituting formulas (16), (17), and (18) into formula (12), we obtain:

[0105] (19)

[0106] Formula (19) is the first form of the differential equation obtained in step S21, where u is the radial deformation of the ring.

[0107] In step S22, if only one pair of radial forces P is applied to the ring, then , the deflection curve equation (19) becomes:

[0108] (20)

[0109] Formula (20) is the second form of the differential equation obtained in step S22.

[0110] In step S23, considering that the pipe generally needs to withstand an internal negative pressure of 0.1 MPa during testing, a coefficient m is introduced, namely:

[0111] (twenty one)

[0112] For water supply pipes, if a fault occurs during actual use, such as a burst pipe, a certain negative pressure will be formed inside the pipe. Therefore, when testing the pipe, a negative pressure will be created inside the pipe to ensure that the pipe performance meets the standards.

[0113] Formula (21) is the third form of the differential equation obtained in step S23.

[0114] In step S24, the maximum deformation is At the point where the force P acts, the change in the diameter of the ring is the maximum change in the diameter of the ring. u max :

[0115] (twenty two)

[0116] Formula (22) is the third form of the differential equation obtained in step S24.

[0117] Step S3: Calculate the minimum thickness of the base pipe that meets the deformation requirements based on the calculation formula of the maximum radial deformation obtained in step S2. It includes the following steps:

[0118] Step S31: Calculate the parameters of a reference pipe according to the existing shear load formula. The material and outer diameter of the reference pipe are respectively the same as the material and outer diameter of the base pipe.

[0119] Step S32: obtaining the maximum deformation of the reference pipe socket through simulation according to the parameters calculated in step S31.

[0120] Step S33: Substitute the maximum deformation of the socket obtained in step S32 into the calculation formula of step S2 to obtain the coefficient value in the calculation formula, thereby obtaining the calculation formula for the maximum radial deformation of the ring with a known coefficient.

[0121] Step S34: Calculate the minimum thickness of the base pipe socket that meets the deformation requirements according to the national standard allowable deformation regulations and the formula obtained in step S33.

[0122] In step S31, the shear load formula used is derived from the group standard "Corrosion-resistant steel pipe with socket-type flexible joint for water supply and drainage" (T / CISA 108-2021), which is:

[0123] (twenty three)

[0124] like Figure 4 As shown, W is the shear load, in Newton (N); F is the shear force acting on the interface, in Newton (N); M P is the weight of the steel pipe of the test component and the weight of the object in the steel pipe, in kilograms (kg); a is the distance between the shear load application point and the end face of the socket inserted into the socket, in millimeters (mm); b is the distance between the center of gravity of the steel pipe at the socket end and the end face of the socket inserted into the socket, in millimeters (mm); c is the distance between the support point of the pad and the end face of the socket inserted into the socket, in millimeters (mm).

[0125] In this embodiment, the nominal diameter of the base pipe is DN=600mm, and the material is Q235. The nominal diameter of the reference pipe is DN=600mm, and the material is Q235. Its wall thickness is selected according to the provisions of the group standard, and the wall thickness when the nominal pressure is 3.0MPa is selected, that is, the nominal wall thickness S=7mm. At this time, the outer diameter of the base pipe D0=630mm, R=312mm. In addition, the shear force F should not be less than 30 times the nominal diameter DN. In this embodiment, 30 times is taken, that is, F=DN×30=600×30=18000N. The length of the pipe is 1m, c=800mm.

[0126] In this embodiment, the parameters in formula (23) are M P The calculation process of and W is as follows:

[0127]

[0128]

[0129] in, is the density of water, is the density of steel. M P The diameter used in the calculation is the outer diameter D0 of the base pipe, and the calculation error is within the allowable range. In addition, in this embodiment, the material of the pipe socket is Q235, the elastic modulus of the steel pipe material is E=200GPa, and I=S 3 / 12. It should be noted that the calculation formula for the moment of inertia I of the circular tube section also needs to be multiplied by the length, but this solution considers a cylinder of unit length (i.e., the circular ring), so the length is 1.

[0130] Step S31 is thus completed.

[0131] In step S32, based on the parameters obtained by the above calculation, simulation software is used. In this embodiment, the maximum deformation of the socket of the reference pipe is simulated by finite element simulation. u max =12.19 mm. During simulation, the material parameter Poisson's ratio = 0.3. The simulation method is well known to those skilled in the art and will not be described in detail here.

[0132] In step S33, u max =12.19 Substituting into formula (22), we get m=1.18 (Note: When calculating, the units of length are meters, and the unit of elastic modulus E is Pa). Thus, we get:

[0133] (twenty four)

[0134] From formula (24), we can see that umax The value is related to the pipe diameter and pipe thickness.

[0135] In this embodiment, in step S34, for a pipe with DN=600mm, the national standard stipulates that the allowable deformation must not be greater than 3.6% of the outer diameter of the socket DE=635mm, that is, u max =22.86 mm, and substituting it into formula (24), we can calculate that for a pipe with DN=600 mm, the minimum wall thickness of the socket is S=5.7 mm.

[0136] Table 1 Nominal wall thickness and absolute deformation of DN=600mm pipes at various nominal pressures

[0137]

[0138] In Table 1, each wall thickness is the nominal wall thickness under the corresponding nominal pressure specified in the industry standard, and the absolute deformation is calculated according to formula (24).

[0139] It can be seen from Table 1 that if the base tube purchased by the secondary processing enterprise or user is processed in accordance with the provisions of the industry standard, the base tubes with serial numbers 1, 2, and 3 in Table 1 have a socket thickness greater than 5.7 mm and an absolute deformation less than 22.86 mm, which meet the deformation requirements, while the base tubes with serial numbers 4, 5, and 6 have a socket thickness less than 5.7 mm and an absolute deformation greater than 22.86 mm, which do not meet the deformation requirements.

[0140] If the use requirement of the pipe in a certain occasion is to meet the nominal pressure within 2MPa, the general user will choose the pipe with serial number 4, and will not choose the pipe with serial number 1, 2 or 3 to meet the deformation requirement. Because if one of these three is selected, although it will meet both the strength requirements and the deformation requirements, their thickness is larger and the cost will be much greater than the pipe with serial number 4. If the pipe with serial number 4 is selected, its strength meets the use requirements. For the deformation requirement, some measures can be taken, such as sleeve-fitting an annular reinforcement ring in the socket to increase the thickness of the socket and improve its ability to resist deformation, and this measure is low in cost.

[0141] Finally, it is necessary to explain here that the above embodiments are only used to further illustrate the technical solution of the present invention in detail and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above content of the present invention all fall within the scope of protection of the present invention.

Claims

1. A method for designing the thickness of a socket of a socket-and-spigot pipe, characterized in that: The steps include: Step S1: obtaining the differential equation of radial deformation of the ring and the general solution of the differential equation according to the deflection curve differential equation and the moment balance equation of the ring; Step S2: Calculate and obtain a calculation formula for the maximum radial deformation of the annulus according to the general solution of the differential equation obtained in step S1; the calculation formula contains unknown coefficients, which are introduced in consideration of the internal negative pressure of the pipe during testing and failure; Step S3: The minimum thickness of the socket of the base pipe that meets the deformation requirements is obtained according to the calculation formula of the maximum radial deformation obtained in step S2. In this step, the minimum thickness of the socket that meets the deformation requirements is calculated according to the provisions of the allowable deformation of the pipe and the formula obtained in step S2, including the following steps: Step S31: Calculating parameters of a reference pipe according to an existing shear load formula, wherein the material and outer diameter of the reference pipe are respectively the same as the material and outer diameter of the base pipe; Step S32: obtaining the maximum deformation of the reference pipe socket through simulation according to the parameters calculated in step S31; Step S33: Substituting the maximum deformation of the socket obtained in step S32 into the calculation formula of step S2 to obtain the coefficient value in the calculation formula, thereby obtaining a calculation formula for the maximum radial deformation of the ring with a known coefficient; Step S34: Calculate the minimum thickness of the base pipe socket that meets the deformation requirements according to the national standard allowable deformation regulations and the formula obtained in step S33.

2. The design method according to claim 1, characterized in that: Step S2 includes the following steps: Step S21: Assuming that the annular ring is subjected to at least two radial concentrated forces that are symmetrical relative to the center of the circle, based on the assumption, calculating the constant term in the general solution of the differential equation to obtain the first form of the differential equation; Step S22: Based on the first form of the differential equation obtained in step S21, assuming that the annulus is subjected to only two radial concentrated forces that are symmetrical relative to the center of the circle, the first form of the differential equation is transformed into a second form of the differential equation; Step S23: introducing the internal negative pressure of the annulus into the second form of the differential equation by introducing a coefficient, so as to obtain the third form of the differential equation; Step S24: Obtain a calculation formula for the maximum change in the diameter of the ring with a coefficient according to the third form of the differential equation obtained in step S23.

3. The design method according to claim 1 or 2, characterized in that: In step S1, the radial deformation u The differential equation is: , its general solution is: ； in, R is the average value of the outer circle radius and the inner circle radius of the ring; E is the elastic modulus of the pipe, Pa; I is the moment of inertia of the tube cross section, m 4 ; M is the bending moment borne by a certain section of the ring in the local area, in units of N*m; establish a two-dimensional coordinate system, φ The deformation is u The line connecting the point at and the origin of the coordinate system is the same as the line connecting the point at and the origin of the coordinate system in the two-dimensional coordinate system. x The angle between the positive directions of the axes, ; A1, A2, A3, B2, B3 are constants.

4. The design method according to claim 3, characterized in that: Assuming that the external force on the ring is symmetrical, the deflection curve equation is: .

5. The design method according to claim 4, characterized in that: In step S2, it is assumed that the ring is subjected to at least two radial concentrated forces P that are symmetrical relative to the center of the circle, and the angle between two adjacent radial concentrated forces P is , the ring satisfies the following three boundary conditions: First, in Because of symmetry, The rotation angle of the section at is 0, which satisfies the following formula: ; Second, due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; That is: ; Third, cut near point A, remove point A and the force P, and from the symmetry and equilibrium conditions, we know that the shear force on the section at the circular cut is , that is: ; Combining the above three formulas with the general solution of the differential equation, we get the first form of the differential equation: ； Assuming that the annulus is subjected to only two radial concentrated forces P which are symmetrical relative to the center of the circle, then: , we get the second form of the differential equation: ； Introducing the coefficient m, we get the third form of the differential equation: ； Point of application of force P The point is the point of maximum deformation, and the change in the diameter of the ring is: .

6. The design method according to claim 1, characterized in that: The shear load formula used in step S31 is: ， in: W is the shear load, in N; F is the shear force acting on the interface, in N; M P The weight of the test assembly pipe and the weight of the object in the pipe, in kg; a The distance between the shear load application point and the end face of the socket that has been inserted into the socket, in mm; b It is the distance between the center of gravity of the spigot end pipe and the spigot end face inserted into the socket, in mm; c It is the distance between the support point of the pad and the end face of the socket that has been inserted into the socket, in mm.

7. The design method according to claim 6, characterized in that: F =30×DN, E=200GPa, I=S 3 / 12, where DN is the nominal diameter of the pipe, S is the socket thickness, and the socket thickness used in calculating the coefficient m is the nominal wall thickness under the nominal diameter.

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